Vacuum gripping means which are arranged to permit a limited leakage and in-flow of air at ambient pressure via a restriction to the flow in a suction duct are previously known. These vacuum gripping means are often used in grippers that include a plurality of suction mouths which are distributed over an area and which are supplied from a common vacuum source. The suction mouths may be arranged in rows and columns in the form of an array, e.g., or in the shape of concentric rings, or may be arranged in a singular row. A set of suction mouths are this way connected to a common vacuum chamber in the vacuum gripper which may be realized in different embodiments of plates or beams, e.g.
Vacuum gripping means of this type are suitable for handling of objects which may vary in shape and/or size, e.g., or in the simultaneous handling of several objects such as sets of objects which are to be picked up and released at regular interspaced relation. The restriction to the suction duct flow ensures that a useful work pressure is generated in the vacuum gripper also in a case where one or several suction mouths are inactive and therefore admit a leak flow of ambient pressure into the vacuum chamber.
This technical approach requires surplus capacity with the vacuum source, which typically operates at oversized effect and energy consumption in order to compensate for the loss in efficiency which is caused by the leak flow.
The restriction to flow in the suction duct may be of fixed and invariable type, and thus insensitive to the presence of an object. A drawback in this kind of solution is that evacuation of air from between the gripper and the object via a restricted flow through the suction duct will be relatively time-consuming. Another drawback in relation to a flow that is reduced by means of a fixed restriction in the suction duct is a resulting delay in the process of releasing the object from the gripper. In order to improve the dynamics of the system and to shorten work cycle times, the fixed restriction may be dimensioned to permit a larger leak flow which would obviously require a correspondingly increase in consumption of energy in the vacuum generator.
Another approach aimed to improve the dynamics of the system would be to integrate an object-sensing valve in the suction duct, a valve that on one hand is configured to allow only a limited flow of air in the suction duct when the vacuum gripper is not in contact with an object, and which on the other hand is configured to open the suction duct for unrestricted flow of air when the vacuum gripper is brought into contact with an object, or upon release of an object from the vacuum gripper, respectively.
A previously known object-sensing valve for a vacuum gripper comprises a ball which seals only incompletely against a seat when the ball is sucked towards the seat by an inwardly directed flow, and which falls out from the seat to open the suction duct when the gripper is brought into contact with an object and the flow in result thereof is reduced or ceased. A drawback in relation to this known leak flow valve is that its operation is dependent on the valve's position in space, since the ball is caused by gravitational force to fall out from the seat.